1. The Field of the Invention
The present invention generally relates to semiconductor optical devices. In particular, the present invention relates to a method for optimizing the regrowth over epitaxial layers during manufacture of a distributed feedback laser.
2. The Related Technology
Semiconductor lasers are currently used in a variety of technologies and applications, including communications networks. One type of semiconductor laser is the distributed feedback (“DFB”) laser. The DFB laser produces a stream of coherent, monochromatic light by stimulating photon emission from a solid state material. DFB lasers are commonly used in optical transmitters, which are responsible for modulating electrical signals into optical signals for transmission via an optical communication network.
Generally, a DFB laser includes a positively or negatively doped bottom layer or substrate, and a top layer that is oppositely doped with respect to the bottom layer. An active region, bounded by confinement regions, is included at the junction of the two layers. These structures together form the laser body. A coherent stream of light that is produced in the active region of the DFB laser can be emitted through either longitudinal end, or facet, of the laser body. One facet is typically coated with a high reflective material that redirects photons produced in the active region toward the other facet in order to maximize the emission of coherent light from that facet end. A grating is included in either the top or bottom layer to assist in producing a coherent photon beam. DFB lasers are typically known as single mode devices as they produce light signals at one of several distinct wavelengths, such as 1,310 nm or 1,550 nm. Such light signals are appropriate for use in transmitting information over great distances via an optical communications network.
One challenge relating to DFB and similar lasers involves the deposition of a regrowth layer atop the DFB laser device during manufacture. Typically, such regrowth layers are grown at relatively high temperatures in order to prevent the formation of impurities at the regrowth interface within the laser. These impurities, such as silicon and oxygen, can undesirably compromise the operation of the laser once manufacture and testing are complete.
However, high temperature regrowth can cause damage to the grating layer of the DFB laser by causing it to reflow, which can destroy its structure, rendering the laser unusable.
Therefore, a need exists in the art for a method for control regrowth over epitaxial layers in a DFB laser so as to prevent the formation of impurities therein, while preserving the morphology and integrity of the laser grating.